Snowpack -> Elixir (Phoenix Framework) -> Mix release + wkhtmltopdf

Dockerfile

# ====================================================
# STAGE 1: Snowpack build
FROM node:alpine AS snowpack
WORKDIR /snowpack

# snowpack build
COPY assets ./

# override config
COPY assets/snowpack.config.prod.js ./snowpack.config.js

RUN yarn install
RUN yarn make

# ====================================================
# STAGE 2: Elixir build (mix release)

FROM elixir:1.9.0-alpine AS build
RUN apk add --no-cache build-base
WORKDIR /app

# install hex + rebar
RUN mix local.hex --force && \
    mix local.rebar --force

# set build ENV
ENV MIX_ENV=prod

# install mix dependencies
COPY mix.exs mix.lock ./
COPY config config
RUN mix do deps.get, deps.compile

# copy prebuilt assets and hash it into a digest
COPY --from=snowpack /snowpack/build ./priv/static/
COPY priv priv
RUN mix phx.digest

# compile and build release
COPY lib lib
# uncomment COPY if rel/ exists
# COPY rel rel
RUN mix do compile, release

# ====================================================
# STAGE 3: Production image

# prepare release image
FROM alpine:3.9 AS app
RUN apk add --no-cache openssl ncurses-libs

# ----------------------------------------------------------------------------
# Install wkhtmlpdf from CI
RUN apk add --update --no-cache \
    libgcc libstdc++ libx11 glib libxrender libxext libintl \
    ttf-dejavu ttf-droid ttf-freefont ttf-liberation ttf-ubuntu-font-family

# On alpine static compiled patched qt headless wkhtmltopdf (46.8 MB).
# Compilation took place in Travis CI with auto push to Docker Hub see
# BUILD_LOG env. Checksum is printed in line 13685.
COPY --from=madnight/alpine-wkhtmltopdf-builder:0.12.5-alpine3.10-606718795 \
    /bin/wkhtmltopdf /bin/wkhtmltopdf
ENV BUILD_LOG=https://api.travis-ci.org/v3/job/606718795/log.txt

RUN [ "$(sha256sum /bin/wkhtmltopdf | awk '{ print $1 }')" == \
      "$(wget -q -O - $BUILD_LOG | sed -n '13685p' | awk '{ print $1 }')" ]
# ----------------------------------------------------------------------------

WORKDIR /app

# https://unix.stackexchange.com/questions/186568/what-is-nobody-user-and-group#:~:text=The%20nobody%20user%20is%20a,least%20permissions%20on%20the%20system.
# a user with no login permission (least permission)
RUN chown nobody:nobody /app
USER nobody:nobody

COPY --from=build --chown=nobody:nobody /app/_build/prod/rel/donation ./
ENV HOME=/app
CMD ["bin/donation", "start"]